1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * Read-Copy Update mechanism for mutual exclusion
4 *
5 * Copyright IBM Corporation, 2001
6 *
7 * Author: Dipankar Sarma <dipankar@in.ibm.com>
8 *
9 * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
10 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
11 * Papers:
12 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
13 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
14 *
15 * For detailed explanation of Read-Copy Update mechanism see -
16 * http://lse.sourceforge.net/locking/rcupdate.html
17 *
18 */
19
20#ifndef __LINUX_RCUPDATE_H
21#define __LINUX_RCUPDATE_H
22
23#include <linux/types.h>
24#include <linux/compiler.h>
25#include <linux/atomic.h>
26#include <linux/irqflags.h>
27#include <linux/sched.h>
28#include <linux/bottom_half.h>
29#include <linux/lockdep.h>
30#include <linux/cleanup.h>
31#include <asm/processor.h>
32#include <linux/context_tracking_irq.h>
33
34#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
35#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
36
37#define RCU_SEQ_CTR_SHIFT 2
38#define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1)
39
40/* Exported common interfaces */
41void call_rcu(struct rcu_head *head, rcu_callback_t func);
42void rcu_barrier_tasks(void);
43void synchronize_rcu(void);
44
45struct rcu_gp_oldstate;
46unsigned long get_completed_synchronize_rcu(void);
47void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
48
49// Maximum number of unsigned long values corresponding to
50// not-yet-completed RCU grace periods.
51#define NUM_ACTIVE_RCU_POLL_OLDSTATE 2
52
53/**
54 * same_state_synchronize_rcu - Are two old-state values identical?
55 * @oldstate1: First old-state value.
56 * @oldstate2: Second old-state value.
57 *
58 * The two old-state values must have been obtained from either
59 * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or
60 * get_completed_synchronize_rcu(). Returns @true if the two values are
61 * identical and @false otherwise. This allows structures whose lifetimes
62 * are tracked by old-state values to push these values to a list header,
63 * allowing those structures to be slightly smaller.
64 */
65static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2)
66{
67 return oldstate1 == oldstate2;
68}
69
70#ifdef CONFIG_PREEMPT_RCU
71
72void __rcu_read_lock(void);
73void __rcu_read_unlock(void);
74
75/*
76 * Defined as a macro as it is a very low level header included from
77 * areas that don't even know about current. This gives the rcu_read_lock()
78 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
79 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
80 */
81#define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
82
83#else /* #ifdef CONFIG_PREEMPT_RCU */
84
85#ifdef CONFIG_TINY_RCU
86#define rcu_read_unlock_strict() do { } while (0)
87#else
88void rcu_read_unlock_strict(void);
89#endif
90
91static inline void __rcu_read_lock(void)
92{
93 preempt_disable();
94}
95
96static inline void __rcu_read_unlock(void)
97{
98 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
99 rcu_read_unlock_strict();
100 preempt_enable();
101}
102
103static inline int rcu_preempt_depth(void)
104{
105 return 0;
106}
107
108#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
109
110#ifdef CONFIG_RCU_LAZY
111void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func);
112#else
113static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
114{
115 call_rcu(head, func);
116}
117#endif
118
119/* Internal to kernel */
120void rcu_init(void);
121extern int rcu_scheduler_active;
122void rcu_sched_clock_irq(int user);
123
124#ifdef CONFIG_RCU_STALL_COMMON
125void rcu_sysrq_start(void);
126void rcu_sysrq_end(void);
127#else /* #ifdef CONFIG_RCU_STALL_COMMON */
128static inline void rcu_sysrq_start(void) { }
129static inline void rcu_sysrq_end(void) { }
130#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
131
132#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_VIRT_XFER_TO_GUEST_WORK))
133void rcu_irq_work_resched(void);
134#else
135static __always_inline void rcu_irq_work_resched(void) { }
136#endif
137
138#ifdef CONFIG_RCU_NOCB_CPU
139void rcu_init_nohz(void);
140int rcu_nocb_cpu_offload(int cpu);
141int rcu_nocb_cpu_deoffload(int cpu);
142void rcu_nocb_flush_deferred_wakeup(void);
143
144#define RCU_NOCB_LOCKDEP_WARN(c, s) RCU_LOCKDEP_WARN(c, s)
145
146#else /* #ifdef CONFIG_RCU_NOCB_CPU */
147
148static inline void rcu_init_nohz(void) { }
149static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
150static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
151static inline void rcu_nocb_flush_deferred_wakeup(void) { }
152
153#define RCU_NOCB_LOCKDEP_WARN(c, s)
154
155#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
156
157/*
158 * Note a quasi-voluntary context switch for RCU-tasks's benefit.
159 * This is a macro rather than an inline function to avoid #include hell.
160 */
161#ifdef CONFIG_TASKS_RCU_GENERIC
162
163# ifdef CONFIG_TASKS_RCU
164# define rcu_tasks_classic_qs(t, preempt) \
165 do { \
166 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
167 WRITE_ONCE((t)->rcu_tasks_holdout, false); \
168 } while (0)
169void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
170void synchronize_rcu_tasks(void);
171void rcu_tasks_torture_stats_print(char *tt, char *tf);
172# else
173# define rcu_tasks_classic_qs(t, preempt) do { } while (0)
174# define call_rcu_tasks call_rcu
175# define synchronize_rcu_tasks synchronize_rcu
176# endif
177
178# ifdef CONFIG_TASKS_TRACE_RCU
179// Bits for ->trc_reader_special.b.need_qs field.
180#define TRC_NEED_QS 0x1 // Task needs a quiescent state.
181#define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state.
182
183u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new);
184void rcu_tasks_trace_qs_blkd(struct task_struct *t);
185
186# define rcu_tasks_trace_qs(t) \
187 do { \
188 int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \
189 \
190 if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) && \
191 likely(!___rttq_nesting)) { \
192 rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED); \
193 } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \
194 !READ_ONCE((t)->trc_reader_special.b.blocked)) { \
195 rcu_tasks_trace_qs_blkd(t); \
196 } \
197 } while (0)
198void rcu_tasks_trace_torture_stats_print(char *tt, char *tf);
199# else
200# define rcu_tasks_trace_qs(t) do { } while (0)
201# endif
202
203#define rcu_tasks_qs(t, preempt) \
204do { \
205 rcu_tasks_classic_qs((t), (preempt)); \
206 rcu_tasks_trace_qs(t); \
207} while (0)
208
209# ifdef CONFIG_TASKS_RUDE_RCU
210void synchronize_rcu_tasks_rude(void);
211void rcu_tasks_rude_torture_stats_print(char *tt, char *tf);
212# endif
213
214#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
215void exit_tasks_rcu_start(void);
216void exit_tasks_rcu_finish(void);
217#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
218#define rcu_tasks_classic_qs(t, preempt) do { } while (0)
219#define rcu_tasks_qs(t, preempt) do { } while (0)
220#define rcu_note_voluntary_context_switch(t) do { } while (0)
221#define call_rcu_tasks call_rcu
222#define synchronize_rcu_tasks synchronize_rcu
223static inline void exit_tasks_rcu_start(void) { }
224static inline void exit_tasks_rcu_finish(void) { }
225#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
226
227/**
228 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
229 *
230 * As an accident of implementation, an RCU Tasks Trace grace period also
231 * acts as an RCU grace period. However, this could change at any time.
232 * Code relying on this accident must call this function to verify that
233 * this accident is still happening.
234 *
235 * You have been warned!
236 */
237static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
238
239/**
240 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
241 *
242 * This macro resembles cond_resched(), except that it is defined to
243 * report potential quiescent states to RCU-tasks even if the cond_resched()
244 * machinery were to be shut off, as some advocate for PREEMPTION kernels.
245 */
246#define cond_resched_tasks_rcu_qs() \
247do { \
248 rcu_tasks_qs(current, false); \
249 cond_resched(); \
250} while (0)
251
252/**
253 * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states
254 * @old_ts: jiffies at start of processing.
255 *
256 * This helper is for long-running softirq handlers, such as NAPI threads in
257 * networking. The caller should initialize the variable passed in as @old_ts
258 * at the beginning of the softirq handler. When invoked frequently, this macro
259 * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will
260 * provide both RCU and RCU-Tasks quiescent states. Note that this macro
261 * modifies its old_ts argument.
262 *
263 * Because regions of code that have disabled softirq act as RCU read-side
264 * critical sections, this macro should be invoked with softirq (and
265 * preemption) enabled.
266 *
267 * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would
268 * have more chance to invoke schedule() calls and provide necessary quiescent
269 * states. As a contrast, calling cond_resched() only won't achieve the same
270 * effect because cond_resched() does not provide RCU-Tasks quiescent states.
271 */
272#define rcu_softirq_qs_periodic(old_ts) \
273do { \
274 if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \
275 time_after(jiffies, (old_ts) + HZ / 10)) { \
276 preempt_disable(); \
277 rcu_softirq_qs(); \
278 preempt_enable(); \
279 (old_ts) = jiffies; \
280 } \
281} while (0)
282
283/*
284 * Infrastructure to implement the synchronize_() primitives in
285 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
286 */
287
288#if defined(CONFIG_TREE_RCU)
289#include <linux/rcutree.h>
290#elif defined(CONFIG_TINY_RCU)
291#include <linux/rcutiny.h>
292#else
293#error "Unknown RCU implementation specified to kernel configuration"
294#endif
295
296/*
297 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
298 * are needed for dynamic initialization and destruction of rcu_head
299 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
300 * dynamic initialization and destruction of statically allocated rcu_head
301 * structures. However, rcu_head structures allocated dynamically in the
302 * heap don't need any initialization.
303 */
304#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
305void init_rcu_head(struct rcu_head *head);
306void destroy_rcu_head(struct rcu_head *head);
307void init_rcu_head_on_stack(struct rcu_head *head);
308void destroy_rcu_head_on_stack(struct rcu_head *head);
309#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
310static inline void init_rcu_head(struct rcu_head *head) { }
311static inline void destroy_rcu_head(struct rcu_head *head) { }
312static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
313static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
314#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
315
316#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
317bool rcu_lockdep_current_cpu_online(void);
318#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
319static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
320#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
321
322extern struct lockdep_map rcu_lock_map;
323extern struct lockdep_map rcu_bh_lock_map;
324extern struct lockdep_map rcu_sched_lock_map;
325extern struct lockdep_map rcu_callback_map;
326
327#ifdef CONFIG_DEBUG_LOCK_ALLOC
328
329static inline void rcu_lock_acquire(struct lockdep_map *map)
330{
331 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
332}
333
334static inline void rcu_try_lock_acquire(struct lockdep_map *map)
335{
336 lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_);
337}
338
339static inline void rcu_lock_release(struct lockdep_map *map)
340{
341 lock_release(map, _THIS_IP_);
342}
343
344int debug_lockdep_rcu_enabled(void);
345int rcu_read_lock_held(void);
346int rcu_read_lock_bh_held(void);
347int rcu_read_lock_sched_held(void);
348int rcu_read_lock_any_held(void);
349
350#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
351
352# define rcu_lock_acquire(a) do { } while (0)
353# define rcu_try_lock_acquire(a) do { } while (0)
354# define rcu_lock_release(a) do { } while (0)
355
356static inline int rcu_read_lock_held(void)
357{
358 return 1;
359}
360
361static inline int rcu_read_lock_bh_held(void)
362{
363 return 1;
364}
365
366static inline int rcu_read_lock_sched_held(void)
367{
368 return !preemptible();
369}
370
371static inline int rcu_read_lock_any_held(void)
372{
373 return !preemptible();
374}
375
376static inline int debug_lockdep_rcu_enabled(void)
377{
378 return 0;
379}
380
381#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
382
383#ifdef CONFIG_PROVE_RCU
384
385/**
386 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
387 * @c: condition to check
388 * @s: informative message
389 *
390 * This checks debug_lockdep_rcu_enabled() before checking (c) to
391 * prevent early boot splats due to lockdep not yet being initialized,
392 * and rechecks it after checking (c) to prevent false-positive splats
393 * due to races with lockdep being disabled. See commit 3066820034b5dd
394 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
395 */
396#define RCU_LOCKDEP_WARN(c, s) \
397 do { \
398 static bool __section(".data..unlikely") __warned; \
399 if (debug_lockdep_rcu_enabled() && (c) && \
400 debug_lockdep_rcu_enabled() && !__warned) { \
401 __warned = true; \
402 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
403 } \
404 } while (0)
405
406#ifndef CONFIG_PREEMPT_RCU
407static inline void rcu_preempt_sleep_check(void)
408{
409 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
410 "Illegal context switch in RCU read-side critical section");
411}
412#else // #ifndef CONFIG_PREEMPT_RCU
413static inline void rcu_preempt_sleep_check(void) { }
414#endif // #else // #ifndef CONFIG_PREEMPT_RCU
415
416#define rcu_sleep_check() \
417 do { \
418 rcu_preempt_sleep_check(); \
419 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
420 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
421 "Illegal context switch in RCU-bh read-side critical section"); \
422 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
423 "Illegal context switch in RCU-sched read-side critical section"); \
424 } while (0)
425
426// See RCU_LOCKDEP_WARN() for an explanation of the double call to
427// debug_lockdep_rcu_enabled().
428static inline bool lockdep_assert_rcu_helper(bool c)
429{
430 return debug_lockdep_rcu_enabled() &&
431 (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) &&
432 debug_lockdep_rcu_enabled();
433}
434
435/**
436 * lockdep_assert_in_rcu_read_lock - WARN if not protected by rcu_read_lock()
437 *
438 * Splats if lockdep is enabled and there is no rcu_read_lock() in effect.
439 */
440#define lockdep_assert_in_rcu_read_lock() \
441 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map)))
442
443/**
444 * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh()
445 *
446 * Splats if lockdep is enabled and there is no rcu_read_lock_bh() in effect.
447 * Note that local_bh_disable() and friends do not suffice here, instead an
448 * actual rcu_read_lock_bh() is required.
449 */
450#define lockdep_assert_in_rcu_read_lock_bh() \
451 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map)))
452
453/**
454 * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched()
455 *
456 * Splats if lockdep is enabled and there is no rcu_read_lock_sched()
457 * in effect. Note that preempt_disable() and friends do not suffice here,
458 * instead an actual rcu_read_lock_sched() is required.
459 */
460#define lockdep_assert_in_rcu_read_lock_sched() \
461 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map)))
462
463/**
464 * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader
465 *
466 * Splats if lockdep is enabled and there is no RCU reader of any
467 * type in effect. Note that regions of code protected by things like
468 * preempt_disable, local_bh_disable(), and local_irq_disable() all qualify
469 * as RCU readers.
470 *
471 * Note that this will never trigger in PREEMPT_NONE or PREEMPT_VOLUNTARY
472 * kernels that are not also built with PREEMPT_COUNT. But if you have
473 * lockdep enabled, you might as well also enable PREEMPT_COUNT.
474 */
475#define lockdep_assert_in_rcu_reader() \
476 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) && \
477 !lock_is_held(&rcu_bh_lock_map) && \
478 !lock_is_held(&rcu_sched_lock_map) && \
479 preemptible()))
480
481#else /* #ifdef CONFIG_PROVE_RCU */
482
483#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
484#define rcu_sleep_check() do { } while (0)
485
486#define lockdep_assert_in_rcu_read_lock() do { } while (0)
487#define lockdep_assert_in_rcu_read_lock_bh() do { } while (0)
488#define lockdep_assert_in_rcu_read_lock_sched() do { } while (0)
489#define lockdep_assert_in_rcu_reader() do { } while (0)
490
491#endif /* #else #ifdef CONFIG_PROVE_RCU */
492
493/*
494 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
495 * and rcu_assign_pointer(). Some of these could be folded into their
496 * callers, but they are left separate in order to ease introduction of
497 * multiple pointers markings to match different RCU implementations
498 * (e.g., __srcu), should this make sense in the future.
499 */
500
501#ifdef __CHECKER__
502#define rcu_check_sparse(p, space) \
503 ((void)(((typeof(*p) space *)p) == p))
504#else /* #ifdef __CHECKER__ */
505#define rcu_check_sparse(p, space)
506#endif /* #else #ifdef __CHECKER__ */
507
508#define __unrcu_pointer(p, local) \
509({ \
510 typeof(*p) *local = (typeof(*p) *__force)(p); \
511 rcu_check_sparse(p, __rcu); \
512 ((typeof(*p) __force __kernel *)(local)); \
513})
514/**
515 * unrcu_pointer - mark a pointer as not being RCU protected
516 * @p: pointer needing to lose its __rcu property
517 *
518 * Converts @p from an __rcu pointer to a __kernel pointer.
519 * This allows an __rcu pointer to be used with xchg() and friends.
520 */
521#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
522
523#define __rcu_access_pointer(p, local, space) \
524({ \
525 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
526 rcu_check_sparse(p, space); \
527 ((typeof(*p) __force __kernel *)(local)); \
528})
529#define __rcu_dereference_check(p, local, c, space) \
530({ \
531 /* Dependency order vs. p above. */ \
532 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
533 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
534 rcu_check_sparse(p, space); \
535 ((typeof(*p) __force __kernel *)(local)); \
536})
537#define __rcu_dereference_protected(p, local, c, space) \
538({ \
539 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
540 rcu_check_sparse(p, space); \
541 ((typeof(*p) __force __kernel *)(p)); \
542})
543#define __rcu_dereference_raw(p, local) \
544({ \
545 /* Dependency order vs. p above. */ \
546 typeof(p) local = READ_ONCE(p); \
547 ((typeof(*p) __force __kernel *)(local)); \
548})
549#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
550
551/**
552 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
553 * @v: The value to statically initialize with.
554 */
555#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
556
557/**
558 * rcu_assign_pointer() - assign to RCU-protected pointer
559 * @p: pointer to assign to
560 * @v: value to assign (publish)
561 *
562 * Assigns the specified value to the specified RCU-protected
563 * pointer, ensuring that any concurrent RCU readers will see
564 * any prior initialization.
565 *
566 * Inserts memory barriers on architectures that require them
567 * (which is most of them), and also prevents the compiler from
568 * reordering the code that initializes the structure after the pointer
569 * assignment. More importantly, this call documents which pointers
570 * will be dereferenced by RCU read-side code.
571 *
572 * In some special cases, you may use RCU_INIT_POINTER() instead
573 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
574 * to the fact that it does not constrain either the CPU or the compiler.
575 * That said, using RCU_INIT_POINTER() when you should have used
576 * rcu_assign_pointer() is a very bad thing that results in
577 * impossible-to-diagnose memory corruption. So please be careful.
578 * See the RCU_INIT_POINTER() comment header for details.
579 *
580 * Note that rcu_assign_pointer() evaluates each of its arguments only
581 * once, appearances notwithstanding. One of the "extra" evaluations
582 * is in typeof() and the other visible only to sparse (__CHECKER__),
583 * neither of which actually execute the argument. As with most cpp
584 * macros, this execute-arguments-only-once property is important, so
585 * please be careful when making changes to rcu_assign_pointer() and the
586 * other macros that it invokes.
587 */
588#define rcu_assign_pointer(p, v) \
589do { \
590 uintptr_t _r_a_p__v = (uintptr_t)(v); \
591 rcu_check_sparse(p, __rcu); \
592 \
593 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
594 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
595 else \
596 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
597} while (0)
598
599/**
600 * rcu_replace_pointer() - replace an RCU pointer, returning its old value
601 * @rcu_ptr: RCU pointer, whose old value is returned
602 * @ptr: regular pointer
603 * @c: the lockdep conditions under which the dereference will take place
604 *
605 * Perform a replacement, where @rcu_ptr is an RCU-annotated
606 * pointer and @c is the lockdep argument that is passed to the
607 * rcu_dereference_protected() call used to read that pointer. The old
608 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
609 */
610#define rcu_replace_pointer(rcu_ptr, ptr, c) \
611({ \
612 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
613 rcu_assign_pointer((rcu_ptr), (ptr)); \
614 __tmp; \
615})
616
617/**
618 * rcu_access_pointer() - fetch RCU pointer with no dereferencing
619 * @p: The pointer to read
620 *
621 * Return the value of the specified RCU-protected pointer, but omit the
622 * lockdep checks for being in an RCU read-side critical section. This is
623 * useful when the value of this pointer is accessed, but the pointer is
624 * not dereferenced, for example, when testing an RCU-protected pointer
625 * against NULL. Although rcu_access_pointer() may also be used in cases
626 * where update-side locks prevent the value of the pointer from changing,
627 * you should instead use rcu_dereference_protected() for this use case.
628 * Within an RCU read-side critical section, there is little reason to
629 * use rcu_access_pointer().
630 *
631 * It is usually best to test the rcu_access_pointer() return value
632 * directly in order to avoid accidental dereferences being introduced
633 * by later inattentive changes. In other words, assigning the
634 * rcu_access_pointer() return value to a local variable results in an
635 * accident waiting to happen.
636 *
637 * It is also permissible to use rcu_access_pointer() when read-side
638 * access to the pointer was removed at least one grace period ago, as is
639 * the case in the context of the RCU callback that is freeing up the data,
640 * or after a synchronize_rcu() returns. This can be useful when tearing
641 * down multi-linked structures after a grace period has elapsed. However,
642 * rcu_dereference_protected() is normally preferred for this use case.
643 */
644#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
645
646/**
647 * rcu_dereference_check() - rcu_dereference with debug checking
648 * @p: The pointer to read, prior to dereferencing
649 * @c: The conditions under which the dereference will take place
650 *
651 * Do an rcu_dereference(), but check that the conditions under which the
652 * dereference will take place are correct. Typically the conditions
653 * indicate the various locking conditions that should be held at that
654 * point. The check should return true if the conditions are satisfied.
655 * An implicit check for being in an RCU read-side critical section
656 * (rcu_read_lock()) is included.
657 *
658 * For example:
659 *
660 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
661 *
662 * could be used to indicate to lockdep that foo->bar may only be dereferenced
663 * if either rcu_read_lock() is held, or that the lock required to replace
664 * the bar struct at foo->bar is held.
665 *
666 * Note that the list of conditions may also include indications of when a lock
667 * need not be held, for example during initialisation or destruction of the
668 * target struct:
669 *
670 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
671 * atomic_read(&foo->usage) == 0);
672 *
673 * Inserts memory barriers on architectures that require them
674 * (currently only the Alpha), prevents the compiler from refetching
675 * (and from merging fetches), and, more importantly, documents exactly
676 * which pointers are protected by RCU and checks that the pointer is
677 * annotated as __rcu.
678 */
679#define rcu_dereference_check(p, c) \
680 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
681 (c) || rcu_read_lock_held(), __rcu)
682
683/**
684 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
685 * @p: The pointer to read, prior to dereferencing
686 * @c: The conditions under which the dereference will take place
687 *
688 * This is the RCU-bh counterpart to rcu_dereference_check(). However,
689 * please note that starting in v5.0 kernels, vanilla RCU grace periods
690 * wait for local_bh_disable() regions of code in addition to regions of
691 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means
692 * that synchronize_rcu(), call_rcu, and friends all take not only
693 * rcu_read_lock() but also rcu_read_lock_bh() into account.
694 */
695#define rcu_dereference_bh_check(p, c) \
696 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
697 (c) || rcu_read_lock_bh_held(), __rcu)
698
699/**
700 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
701 * @p: The pointer to read, prior to dereferencing
702 * @c: The conditions under which the dereference will take place
703 *
704 * This is the RCU-sched counterpart to rcu_dereference_check().
705 * However, please note that starting in v5.0 kernels, vanilla RCU grace
706 * periods wait for preempt_disable() regions of code in addition to
707 * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
708 * This means that synchronize_rcu(), call_rcu, and friends all take not
709 * only rcu_read_lock() but also rcu_read_lock_sched() into account.
710 */
711#define rcu_dereference_sched_check(p, c) \
712 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
713 (c) || rcu_read_lock_sched_held(), \
714 __rcu)
715
716/**
717 * rcu_dereference_all_check() - rcu_dereference_all with debug checking
718 * @p: The pointer to read, prior to dereferencing
719 * @c: The conditions under which the dereference will take place
720 *
721 * This is similar to rcu_dereference_check(), but allows protection
722 * by all forms of vanilla RCU readers, including preemption disabled,
723 * bh-disabled, and interrupt-disabled regions of code. Note that "vanilla
724 * RCU" excludes SRCU and the various Tasks RCU flavors. Please note
725 * that this macro should not be backported to any Linux-kernel version
726 * preceding v5.0 due to changes in synchronize_rcu() semantics prior
727 * to that version.
728 */
729#define rcu_dereference_all_check(p, c) \
730 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
731 (c) || rcu_read_lock_any_held(), \
732 __rcu)
733
734/*
735 * The tracing infrastructure traces RCU (we want that), but unfortunately
736 * some of the RCU checks causes tracing to lock up the system.
737 *
738 * The no-tracing version of rcu_dereference_raw() must not call
739 * rcu_read_lock_held().
740 */
741#define rcu_dereference_raw_check(p) \
742 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
743
744/**
745 * rcu_dereference_protected() - fetch RCU pointer when updates prevented
746 * @p: The pointer to read, prior to dereferencing
747 * @c: The conditions under which the dereference will take place
748 *
749 * Return the value of the specified RCU-protected pointer, but omit
750 * the READ_ONCE(). This is useful in cases where update-side locks
751 * prevent the value of the pointer from changing. Please note that this
752 * primitive does *not* prevent the compiler from repeating this reference
753 * or combining it with other references, so it should not be used without
754 * protection of appropriate locks.
755 *
756 * This function is only for update-side use. Using this function
757 * when protected only by rcu_read_lock() will result in infrequent
758 * but very ugly failures.
759 */
760#define rcu_dereference_protected(p, c) \
761 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
762
763
764/**
765 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
766 * @p: The pointer to read, prior to dereferencing
767 *
768 * This is a simple wrapper around rcu_dereference_check().
769 */
770#define rcu_dereference(p) rcu_dereference_check(p, 0)
771
772/**
773 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
774 * @p: The pointer to read, prior to dereferencing
775 *
776 * Makes rcu_dereference_check() do the dirty work.
777 */
778#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
779
780/**
781 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
782 * @p: The pointer to read, prior to dereferencing
783 *
784 * Makes rcu_dereference_check() do the dirty work.
785 */
786#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
787
788/**
789 * rcu_dereference_all() - fetch RCU-all-protected pointer for dereferencing
790 * @p: The pointer to read, prior to dereferencing
791 *
792 * Makes rcu_dereference_check() do the dirty work.
793 */
794#define rcu_dereference_all(p) rcu_dereference_all_check(p, 0)
795
796/**
797 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
798 * @p: The pointer to hand off
799 *
800 * This is simply an identity function, but it documents where a pointer
801 * is handed off from RCU to some other synchronization mechanism, for
802 * example, reference counting or locking. In C11, it would map to
803 * kill_dependency(). It could be used as follows::
804 *
805 * rcu_read_lock();
806 * p = rcu_dereference(gp);
807 * long_lived = is_long_lived(p);
808 * if (long_lived) {
809 * if (!atomic_inc_not_zero(p->refcnt))
810 * long_lived = false;
811 * else
812 * p = rcu_pointer_handoff(p);
813 * }
814 * rcu_read_unlock();
815 */
816#define rcu_pointer_handoff(p) (p)
817
818/**
819 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
820 *
821 * When synchronize_rcu() is invoked on one CPU while other CPUs
822 * are within RCU read-side critical sections, then the
823 * synchronize_rcu() is guaranteed to block until after all the other
824 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
825 * on one CPU while other CPUs are within RCU read-side critical
826 * sections, invocation of the corresponding RCU callback is deferred
827 * until after the all the other CPUs exit their critical sections.
828 *
829 * Both synchronize_rcu() and call_rcu() also wait for regions of code
830 * with preemption disabled, including regions of code with interrupts or
831 * softirqs disabled.
832 *
833 * Note, however, that RCU callbacks are permitted to run concurrently
834 * with new RCU read-side critical sections. One way that this can happen
835 * is via the following sequence of events: (1) CPU 0 enters an RCU
836 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
837 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
838 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
839 * callback is invoked. This is legal, because the RCU read-side critical
840 * section that was running concurrently with the call_rcu() (and which
841 * therefore might be referencing something that the corresponding RCU
842 * callback would free up) has completed before the corresponding
843 * RCU callback is invoked.
844 *
845 * RCU read-side critical sections may be nested. Any deferred actions
846 * will be deferred until the outermost RCU read-side critical section
847 * completes.
848 *
849 * You can avoid reading and understanding the next paragraph by
850 * following this rule: don't put anything in an rcu_read_lock() RCU
851 * read-side critical section that would block in a !PREEMPTION kernel.
852 * But if you want the full story, read on!
853 *
854 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
855 * it is illegal to block while in an RCU read-side critical section.
856 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
857 * kernel builds, RCU read-side critical sections may be preempted,
858 * but explicit blocking is illegal. Finally, in preemptible RCU
859 * implementations in real-time (with -rt patchset) kernel builds, RCU
860 * read-side critical sections may be preempted and they may also block, but
861 * only when acquiring spinlocks that are subject to priority inheritance.
862 */
863static __always_inline void rcu_read_lock(void)
864{
865 __rcu_read_lock();
866 __acquire(RCU);
867 rcu_lock_acquire(&rcu_lock_map);
868 RCU_LOCKDEP_WARN(!rcu_is_watching(),
869 "rcu_read_lock() used illegally while idle");
870}
871
872/*
873 * So where is rcu_write_lock()? It does not exist, as there is no
874 * way for writers to lock out RCU readers. This is a feature, not
875 * a bug -- this property is what provides RCU's performance benefits.
876 * Of course, writers must coordinate with each other. The normal
877 * spinlock primitives work well for this, but any other technique may be
878 * used as well. RCU does not care how the writers keep out of each
879 * others' way, as long as they do so.
880 */
881
882/**
883 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
884 *
885 * In almost all situations, rcu_read_unlock() is immune from deadlock.
886 * This deadlock immunity also extends to the scheduler's runqueue
887 * and priority-inheritance spinlocks, courtesy of the quiescent-state
888 * deferral that is carried out when rcu_read_unlock() is invoked with
889 * interrupts disabled.
890 *
891 * See rcu_read_lock() for more information.
892 */
893static inline void rcu_read_unlock(void)
894{
895 RCU_LOCKDEP_WARN(!rcu_is_watching(),
896 "rcu_read_unlock() used illegally while idle");
897 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
898 __release(RCU);
899 __rcu_read_unlock();
900}
901
902/**
903 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
904 *
905 * This is equivalent to rcu_read_lock(), but also disables softirqs.
906 * Note that anything else that disables softirqs can also serve as an RCU
907 * read-side critical section. However, please note that this equivalence
908 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and
909 * rcu_read_lock_bh() were unrelated.
910 *
911 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
912 * must occur in the same context, for example, it is illegal to invoke
913 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
914 * was invoked from some other task.
915 */
916static inline void rcu_read_lock_bh(void)
917{
918 local_bh_disable();
919 __acquire(RCU_BH);
920 rcu_lock_acquire(&rcu_bh_lock_map);
921 RCU_LOCKDEP_WARN(!rcu_is_watching(),
922 "rcu_read_lock_bh() used illegally while idle");
923}
924
925/**
926 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
927 *
928 * See rcu_read_lock_bh() for more information.
929 */
930static inline void rcu_read_unlock_bh(void)
931{
932 RCU_LOCKDEP_WARN(!rcu_is_watching(),
933 "rcu_read_unlock_bh() used illegally while idle");
934 rcu_lock_release(&rcu_bh_lock_map);
935 __release(RCU_BH);
936 local_bh_enable();
937}
938
939/**
940 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
941 *
942 * This is equivalent to rcu_read_lock(), but also disables preemption.
943 * Read-side critical sections can also be introduced by anything else that
944 * disables preemption, including local_irq_disable() and friends. However,
945 * please note that the equivalence to rcu_read_lock() applies only to
946 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
947 * were unrelated.
948 *
949 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
950 * must occur in the same context, for example, it is illegal to invoke
951 * rcu_read_unlock_sched() from process context if the matching
952 * rcu_read_lock_sched() was invoked from an NMI handler.
953 */
954static inline void rcu_read_lock_sched(void)
955{
956 preempt_disable();
957 __acquire(RCU_SCHED);
958 rcu_lock_acquire(&rcu_sched_lock_map);
959 RCU_LOCKDEP_WARN(!rcu_is_watching(),
960 "rcu_read_lock_sched() used illegally while idle");
961}
962
963/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
964static inline notrace void rcu_read_lock_sched_notrace(void)
965{
966 preempt_disable_notrace();
967 __acquire(RCU_SCHED);
968}
969
970/**
971 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
972 *
973 * See rcu_read_lock_sched() for more information.
974 */
975static inline void rcu_read_unlock_sched(void)
976{
977 RCU_LOCKDEP_WARN(!rcu_is_watching(),
978 "rcu_read_unlock_sched() used illegally while idle");
979 rcu_lock_release(&rcu_sched_lock_map);
980 __release(RCU_SCHED);
981 preempt_enable();
982}
983
984/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
985static inline notrace void rcu_read_unlock_sched_notrace(void)
986{
987 __release(RCU_SCHED);
988 preempt_enable_notrace();
989}
990
991static __always_inline void rcu_read_lock_dont_migrate(void)
992{
993 if (IS_ENABLED(CONFIG_PREEMPT_RCU))
994 migrate_disable();
995 rcu_read_lock();
996}
997
998static inline void rcu_read_unlock_migrate(void)
999{
1000 rcu_read_unlock();
1001 if (IS_ENABLED(CONFIG_PREEMPT_RCU))
1002 migrate_enable();
1003}
1004
1005/**
1006 * RCU_INIT_POINTER() - initialize an RCU protected pointer
1007 * @p: The pointer to be initialized.
1008 * @v: The value to initialized the pointer to.
1009 *
1010 * Initialize an RCU-protected pointer in special cases where readers
1011 * do not need ordering constraints on the CPU or the compiler. These
1012 * special cases are:
1013 *
1014 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
1015 * 2. The caller has taken whatever steps are required to prevent
1016 * RCU readers from concurrently accessing this pointer *or*
1017 * 3. The referenced data structure has already been exposed to
1018 * readers either at compile time or via rcu_assign_pointer() *and*
1019 *
1020 * a. You have not made *any* reader-visible changes to
1021 * this structure since then *or*
1022 * b. It is OK for readers accessing this structure from its
1023 * new location to see the old state of the structure. (For
1024 * example, the changes were to statistical counters or to
1025 * other state where exact synchronization is not required.)
1026 *
1027 * Failure to follow these rules governing use of RCU_INIT_POINTER() will
1028 * result in impossible-to-diagnose memory corruption. As in the structures
1029 * will look OK in crash dumps, but any concurrent RCU readers might
1030 * see pre-initialized values of the referenced data structure. So
1031 * please be very careful how you use RCU_INIT_POINTER()!!!
1032 *
1033 * If you are creating an RCU-protected linked structure that is accessed
1034 * by a single external-to-structure RCU-protected pointer, then you may
1035 * use RCU_INIT_POINTER() to initialize the internal RCU-protected
1036 * pointers, but you must use rcu_assign_pointer() to initialize the
1037 * external-to-structure pointer *after* you have completely initialized
1038 * the reader-accessible portions of the linked structure.
1039 *
1040 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
1041 * ordering guarantees for either the CPU or the compiler.
1042 */
1043#define RCU_INIT_POINTER(p, v) \
1044 do { \
1045 rcu_check_sparse(p, __rcu); \
1046 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1047 } while (0)
1048
1049/**
1050 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
1051 * @p: The pointer to be initialized.
1052 * @v: The value to initialized the pointer to.
1053 *
1054 * GCC-style initialization for an RCU-protected pointer in a structure field.
1055 */
1056#define RCU_POINTER_INITIALIZER(p, v) \
1057 .p = RCU_INITIALIZER(v)
1058
1059/**
1060 * kfree_rcu() - kfree an object after a grace period.
1061 * @ptr: pointer to kfree for double-argument invocations.
1062 * @rhf: the name of the struct rcu_head within the type of @ptr.
1063 *
1064 * Many rcu callbacks functions just call kfree() on the base structure.
1065 * These functions are trivial, but their size adds up, and furthermore
1066 * when they are used in a kernel module, that module must invoke the
1067 * high-latency rcu_barrier() function at module-unload time.
1068 *
1069 * The kfree_rcu() function handles this issue. In order to have a universal
1070 * callback function handling different offsets of rcu_head, the callback needs
1071 * to determine the starting address of the freed object, which can be a large
1072 * kmalloc or vmalloc allocation. To allow simply aligning the pointer down to
1073 * page boundary for those, only offsets up to 4095 bytes can be accommodated.
1074 * If the offset is larger than 4095 bytes, a compile-time error will
1075 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
1076 * either fall back to use of call_rcu() or rearrange the structure to
1077 * position the rcu_head structure into the first 4096 bytes.
1078 *
1079 * The object to be freed can be allocated either by kmalloc() or
1080 * kmem_cache_alloc().
1081 *
1082 * Note that the allowable offset might decrease in the future.
1083 *
1084 * The BUILD_BUG_ON check must not involve any function calls, hence the
1085 * checks are done in macros here.
1086 */
1087#define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
1088#define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
1089
1090/**
1091 * kfree_rcu_mightsleep() - kfree an object after a grace period.
1092 * @ptr: pointer to kfree for single-argument invocations.
1093 *
1094 * When it comes to head-less variant, only one argument
1095 * is passed and that is just a pointer which has to be
1096 * freed after a grace period. Therefore the semantic is
1097 *
1098 * kfree_rcu_mightsleep(ptr);
1099 *
1100 * where @ptr is the pointer to be freed by kvfree().
1101 *
1102 * Please note, head-less way of freeing is permitted to
1103 * use from a context that has to follow might_sleep()
1104 * annotation. Otherwise, please switch and embed the
1105 * rcu_head structure within the type of @ptr.
1106 */
1107#define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1108#define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
1109
1110/*
1111 * In mm/slab_common.c, no suitable header to include here.
1112 */
1113void kvfree_call_rcu(struct rcu_head *head, void *ptr);
1114
1115/*
1116 * The BUILD_BUG_ON() makes sure the rcu_head offset can be handled. See the
1117 * comment of kfree_rcu() for details.
1118 */
1119#define kvfree_rcu_arg_2(ptr, rhf) \
1120do { \
1121 typeof (ptr) ___p = (ptr); \
1122 \
1123 if (___p) { \
1124 BUILD_BUG_ON(offsetof(typeof(*(ptr)), rhf) >= 4096); \
1125 kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \
1126 } \
1127} while (0)
1128
1129#define kvfree_rcu_arg_1(ptr) \
1130do { \
1131 typeof(ptr) ___p = (ptr); \
1132 \
1133 if (___p) \
1134 kvfree_call_rcu(NULL, (void *) (___p)); \
1135} while (0)
1136
1137/*
1138 * Place this after a lock-acquisition primitive to guarantee that
1139 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
1140 * if the UNLOCK and LOCK are executed by the same CPU or if the
1141 * UNLOCK and LOCK operate on the same lock variable.
1142 */
1143#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
1144#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
1145#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1146#define smp_mb__after_unlock_lock() do { } while (0)
1147#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
1148
1149
1150/* Has the specified rcu_head structure been handed to call_rcu()? */
1151
1152/**
1153 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
1154 * @rhp: The rcu_head structure to initialize.
1155 *
1156 * If you intend to invoke rcu_head_after_call_rcu() to test whether a
1157 * given rcu_head structure has already been passed to call_rcu(), then
1158 * you must also invoke this rcu_head_init() function on it just after
1159 * allocating that structure. Calls to this function must not race with
1160 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
1161 */
1162static inline void rcu_head_init(struct rcu_head *rhp)
1163{
1164 rhp->func = (rcu_callback_t)~0L;
1165}
1166
1167/**
1168 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
1169 * @rhp: The rcu_head structure to test.
1170 * @f: The function passed to call_rcu() along with @rhp.
1171 *
1172 * Returns @true if the @rhp has been passed to call_rcu() with @func,
1173 * and @false otherwise. Emits a warning in any other case, including
1174 * the case where @rhp has already been invoked after a grace period.
1175 * Calls to this function must not race with callback invocation. One way
1176 * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
1177 * in an RCU read-side critical section that includes a read-side fetch
1178 * of the pointer to the structure containing @rhp.
1179 */
1180static inline bool
1181rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1182{
1183 rcu_callback_t func = READ_ONCE(rhp->func);
1184
1185 if (func == f)
1186 return true;
1187 WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1188 return false;
1189}
1190
1191/* kernel/ksysfs.c definitions */
1192extern int rcu_expedited;
1193extern int rcu_normal;
1194
1195DEFINE_LOCK_GUARD_0(rcu,
1196 do {
1197 rcu_read_lock();
1198 /*
1199 * sparse doesn't call the cleanup function,
1200 * so just release immediately and don't track
1201 * the context. We don't need to anyway, since
1202 * the whole point of the guard is to not need
1203 * the explicit unlock.
1204 */
1205 __release(RCU);
1206 } while (0),
1207 rcu_read_unlock())
1208
1209#endif /* __LINUX_RCUPDATE_H */
1210